This invention relates to multi-piece golf balls of at least four layers including a solid core, a surrounding layer, an intermediate layer and a cover, which are improved in feel, control, durability and flight performance.
In the past, a variety of improvements were made on wound golf balls and solid golf balls. One typical attempt is to optimize the gage and hardness of the core and cover of a two-piece solid golf ball.
While most prior art solid golf balls have a two-layer structure consisting of a solid core and a cover, the recent trend has moved to a multilayer structure having an intermediate layer disposed between the solid core and the cover. Many attempts have been made to optimize the respective layers. Typical examples are disclosed in JP-A 9-266959, JP-A 10-127818 and JP-A 10-127819. These proposals intend to improve the feel and controllability of a golf ball by constructing the ball to a multilayer structure including an internal layer, an intermediate layer and a shell layer while providing a hardness difference between the adjacent layers. In a situation where a large hardness difference is set between the adjacent layers, if the gages and materials of the respective layers are not adequate, the respective layers undergo a largely differing deformation upon shots, yielding an energy loss at each interface between adjacent layers. This can result in losses of rebound, distance and durability. The problem becomes outstanding particularly when the bond between adjacent layers is weak.
An attempt is then made to solve the above problem by reducing the hardness difference between the adjacent layers. This attempt, however, sacrifices the feel-improving effects.
Therefor, the optimization associated with the multilayer construction of a golf ball is very difficult. There is a need for a golf ball of multilayer structure in which the respective layers are optimized so as to give a good profile of feel, control, durability and flight performance.
An object of the invention is to provide a multi-piece golf ball of at least four layers including a solid core, a surrounding layer, an intermediate layer and a cover, which is improved in feel, controllability, durability and flight performance.
Regarding a golf ball comprising a solid core, a surrounding layer, an intermediate layer and a cover, the inventor has attempted to use a heated mixture of any one of the following compositions (1), (2) and (3) and having a melt index of at least 1 dg/min as the material of which the surrounding layer, the intermediate layer and/or the cover is made.
Composition (1) comprising the following:
(a) 100 parts by weight of an olefin-unsaturated carboxylic acid random copolymer and/or an olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer,
(b) 5 to 80 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 280, and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (a) and (b).
Composition (2) comprising the following:
(d) 100 parts by weight of a metal ion-neutralized olefin-unsaturated carboxylic acid random copolymer and/or a metal ion-neutralized olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer,
(b) 5 to 80 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 280, and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (d) and (b).
Composition (3) comprising the following:
100 parts by weight of a mixture of (a) an olefin-unsaturated carboxylic acid random copolymer and/or an olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer and (d) a metal ion-neutralized olefin-unsaturated carboxylic acid random copolymer and/or a metal ion-neutralized olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer,
(b) 5 to 80 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 280, and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (a), (d) and (b).
It has been found that the multi-piece golf ball whose surrounding layer, intermediate layer or cover is formed of the above-formulated material is improved in rebound and flight distance. This improvement in rebound leads to the advantage that there is left a room for further improvements in feel, controllability and durability.
Continuing investigations in order to take the advantage to a full extent, the inventor has found that the improvement in rebound contributes to a softening of feel, and with respect to controllability, the same allows the cover to be softened so that an increased spin receptivity is expectable, and that durability is improved by optimizing the hardness distribution among the surrounding layer, the intermediate layer and the cover.
More specifically, the hardnesses of the respective layers of the multi-piece golf ball are such that the surrounding layer has a Shore D hardness of 10 to 55, the intermediate layer has a Shore D hardness of 40 to 63, the cover has a Shore D hardness of 45 to 68, the Shore D hardness of the surrounding layer is not greater than the Shore D hardness of the intermediate layer, which is not greater than the Shore D hardness of the cover. When the ball is hit, the ball receives the impact force over its entirety, rather than local concentration of the impact force, so that the energy loss associated with ball deformation is minimized. This leads to durability, good rebound or restitution, an increase of travel distance and a soft feel. Additionally, the cover can be made so soft that spin receptivity is increased to provide for good controllability. The present invention is predicated on these findings.
In a first aspect, the invention provides a multi-piece golf ball comprising a solid core, a surrounding layer enclosing the solid core, an intermediate layer enclosing the surrounding layer, and a cover enclosing the intermediate layer, wherein
at least one of the surrounding layer, the intermediate layer and the cover is formed of a heated mixture comprising
(a) 100 parts by weight of an olefin-unsaturated carboxylic acid random copolymer and/or an olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer,
(b) 5 to 80 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 280, and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (a) and (b), the heated mixture having a melt index of at least 1.0 dg/min,
the surrounding layer has a Shore D hardness of 10 to 55, the intermediate layer has a Shore D hardness of 40 to 63, the cover has a Shore D hardness of 45 to 68, the Shore D hardness of the surrounding layer is not greater than the Shore D hardness of the intermediate layer, which is not greater than the Shore D hardness of the cover.
In a second aspect, the invention provides a multi-piece golf ball comprising a solid core, a surrounding layer enclosing the solid core, an intermediate layer enclosing the surrounding layer, and a cover enclosing the intermediate layer, wherein
at least one of the surrounding layer, the intermediate layer and the cover is formed of a heated mixture comprising
(d) 100 parts by weight of a metal ion-neutralized olefin-unsaturated carboxylic acid random copolymer and/or a metal ion-neutralized olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer,
(b) 5 to 80 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 280, and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (d) and (b), the heated mixture having a melt index of at least 1.0 dg/min,
the surrounding layer has a Shore D hardness of 10 to 55, the intermediate layer has a Shore D hardness of 40 to 63, the cover has a Shore D hardness of 45 to 68, the Shore D hardness of the surrounding layer is not greater than the Shore D hardness of the intermediate layer, which is not greater than the Shore D hardness of the cover.
In a third aspect, the invention provides a multi-piece golf ball comprising a solid core, a surrounding layer enclosing the solid core, an intermediate layer enclosing the surrounding layer, and a cover enclosing the intermediate layer, wherein
at least one of the surrounding layer, the intermediate layer and the cover is formed of a heated mixture comprising
100 parts by weight of a mixture of (a) an olefin-unsaturated carboxylic acid random copolymer and/or an olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer and (d) a metal ion-neutralized olefin-unsaturated carboxylic acid random copolymer and/or a metal ion-neutralized olefin-unsaturated carboxylic acid-unsaturated carboxylate random copolymer,
(b) 5 to 80 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 280, and
(c) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (a), (d) and (b), the heated mixture having a melt index of at least 1.0 dg/min,
the surrounding layer has a Shore D hardness of 10 to 55, the intermediate layer has a Shore D hardness of 40 to 63, the cover has a Shore D hardness of 45 to 68, the Shore D hardness of the surrounding layer is not greater than the Shore D hardness of the intermediate layer, which is not greater than the Shore D hardness of the cover.
In one preferred embodiment, the solid core is formed of a polybutadiene-based rubber composition and has a diameter of 22 to 38 mm and a deflection of 2.5 to 7.0 mm under an applied load of 100 kg.
In another preferred embodiment, the surrounding layer has a gage of 0.3 to 3.0 mm, the intermediate layer has a gage of 0.3 to 3.0 mm, the cover has a gage of 0.3 to 3.0 mm, and the total gage of the surrounding layer, the intermediate layer and the cover is at least 1.5 mm.
Also preferably, the surrounding layer is formed mainly of at least one elastomer selected from among thermoplastic polyester elastomers, thermoplastic polyurethane elastomers, and thermoplastic polyamide elastomers.